1. Field of the Invention
The present invention relates to compressor aftercooler bypass systems and, more particularly, to an aftercooler bypass having integral water separator.
2. Description of the Related Art
Railway braking systems rely on, among other things, air compressors to generate the compressed air of the pneumatic braking system. As the compression of air results in heating of the air to temperatures that are too hot for braking systems, railway air compressors are generally provided with an aftercooler to cool the compressed air to 20° F. to 40° F. above ambient temperature. The cooled, compressed air is then supplied to the air supply system of a locomotive through a compressor discharge pipe that connects to the first main reservoir. This discharge pipe may be as long as 30 feet, and may necessarily include several ninety degree bends. In winter operation, when the ambient air temperature can be well below freezing (32° F.), water vapor and water aerosol in the compressed air stream can freeze in the compressor discharge pipe, thereby at least partially blocking the flow of air to the braking system and adversely interfering with the operation of the braking system.
As is well known to those skilled in the art, and described by a body of knowledge known as psychrometrics, the maximum total amount of water vapor in a volume of air is strongly dependent on the air temperature, as warm air is able to hold much more water vapor than cool air. This effect is characterized as the partial pressure saturation pressure. Further, as is also well known, the water vapor saturation partial pressure is the maximum water vapor in air at that temperature, regardless of air pressure. As air is compressed, the water vapor in the air will also be compressed, until the water vapor partial pressure equals the saturation pressure. The net result is that for a railway compressor with a 10.5:1 compression ratio, intake air as dry as 9.5 percent relative humidity will be at 100 percent relative humidity after compression. Lastly, due to the thermodynamics of air, the temperature of the air increases significantly as a result of compression. For a two-stage railway compressor, the second stage discharge temperature may be as high as 300° F. above ambient temperature.
Thus, based on the temperature dependent water vapor holding capacity of air and the effect of the compression on the water holding capacity of the air, the hot air discharged from the second stage of an air compressor may contain a significant amount of water vapor. As this hot air flows through a compressor aftercooler, the air temperature is reduced to 20° F. to 40° F. above ambient temperature. Air at this temperature can hold much less water vapor than air at the second stage discharge temperature, so the excess water vapor precipitates out as liquid water and/or water aerosol. When this liquid water is transported into the compressor discharge pipe, it may freeze if the discharge pipe and ambient air are cold enough. In addition, because the air exiting the compressor is 20° F. to 40° F. above ambient air temperature, it is subject to further cooling in the compressor discharge pipe. As the air temperature drops in the pipe, further water will precipitate out thereby compounding the problem.